Synthesis and in vitro activity evaluation of 2',3'-c-dimethyl carbocyclic nucleoside analogues as potential anti-HCV agents

Article abstract of DOI:10.1080/15257770903155642

The first synthetic route of novel 2'(β),3'(β)-C-dimethyl carbodine analogues is described. The key intermediate cyclopentenyl alcohol 11(β) prepared from Weinreb amide 4 via ring-closing metathesis (RCM) and vicinal dihydroxylation. Coupling of 12 with n

Full text of DOI:10.1080/15257770903155642

Nucleosides, Nucleotides and Nucleic Acids, 28:761–771, 2009
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770903155642
SYNTHESIS AND IN VITRO ACTIVITY EVALUATION OF
ꢀ
ꢀ
2
,3 -C-DIMETHYL CARBOCYCLIC NUCLEOSIDE ANALOGUES
AS POTENTIAL ANTI-HCV AGENTS
Ok Hyun Ko and Joon Hee Hong
BK21-Project Team, College of Pharmacy, Chosun University, Kwangju, Republic of Korea
ꢁ
ꢁ
2
The first synthetic route of novel 2 (β),3 (β)-C-dimethyl carbodine analogues is described. The
key intermediate cyclopentenyl alcohol 11(β) prepared from Weinreb amide 4 via ring-closing
metathesis (RCM) and vicinal dihydroxylation. Coupling of 12 with nucleosidic bases via the
Pd(0) catalyzed reaction followed by stereoselective dihydoxylation and deprotection afforded the
target carbocyclic nucleoside analogues. The synthesized compounds were evaluated as inhibitors of
the hepatitis C virus (HCV) in Huh-7 cell line in vitro. However, the nucleosides failed to inhibit
HCV RNA replication in the cell-based replicon assay (EC50 > µM).
Keywords Weinreb amide; carbodine; anti-HCV agents; vicinal dihydroxylation
INTRODUCTION
Hepatitis C virus (HCV) is a single-stranded, enveloped, positive sense
RNA virus in the flaviviridae family.[ The infection of HCV accounts
for major proportions of hepatitis cases worldwide and is also strongly
associated with the development of cirrhosis and hepatocellular carcinoma.
Furthermore, there are no vaccines for the treatment of HCV. The current
standard therapy for chronic HCV infection is interferon-α in combination
with ribavirin; however, this is inadequate because of the low response rates
as well as its side effects.[
1]
2]
The molecular virology of HCV has led to the identification of a
number of antiviral molecular targets, including the NS5B RNA-dependent
RNA polymerase. Inhibition of this enzyme results in the inhibition of the
replication of HCV, making this enzyme crucial target for the development
Received 1 April 2009; accepted 17 June 2009.
This study was supported by research grant of Chosun University, 2008.
Address correspondence to Joon Hee Hong, College of Pharmacy, Chosun University, Kwangju
501-759, Republic of Korea. E-mail: hongjh@chosun.ac.kr
7
61

7
62
O. H. Ko and J. H. Hong
NH2
NH2
N
N
N
N
N
O
O
N
HO
HO
O
CH3
CH3
HO
OH
HO
OH
2
'-C-methyladenosine
2'-C-methylcytidine
1
2
B
HO
H C
3
CH3
HO
OH
1
1
7: B = Adenine
8: B = Cytosine
FIGURE 1 Structure of potent anti-HCV agents.
of new anti-HCV agent. Since nucleoside analogues have been used as a
drug of choice in treating viral infection including, a number of nucleoside
[
3]
analogues have been synthesized and evaluated for anti-HCV agent.
These nucleosides are incorporated into proviral RNA after being converted
to their corresponding triphosphates and act as chain terminators. Modifica-
ꢁ
tion in the vicinity of the 2 -hydroxy of the ribose in natural ribonucleosides
[
4]
can produce effective RNA chain terminator. For example, replacement
of the 2 -hydrogen of natural ribonucleosides with a methyl group yields
ꢁ
ꢁ
compounds with excellent chain-terminating properties. Among them, 2 -C-
methyladenosine[ 1 and 2 -C-methylcytidine 2 were discovered as potent
5]
ꢁ
[6]
anti-HCV agents and are in clinical trials (Figure 1).
In order to explorer the effect of substitution in the sugar moiety of the
aforementioned antiviral agents, we decided to synthesize the nucleoside
ꢁ
ꢁ
analogues 17 and 18 containing a novel 2 ,3 -dimethylcarbasugar. It was of
ꢁ
ꢁ
interest to determine how the two methyl groups at 2 ,3 -position influence
the anti-HCV activity.
As depicted in Scheme 1, we used the Weinreb amide 4 as our starting
[
7]
material which was derived from ethyl glycolate 1.
Conversion of the
amide to the aldehyd 5 was achieved using diisobutylaluminum hydride
(
DIBAL-H). Olefination of 5 with triethyl 2-phosphonopropionate under
[
8]
Horner-Wadsworth-Emmons (HWE) reaction conditions
provided α,β-
unsaturated ethyl ester 6 as cis/trans isomeric mixtures. It is unnecessary
to separate the isomers, because they will be merged into one isomer in the

ꢁ
ꢁ
Synthesis of Novel 2 ,3 -C-Dimethyl Carbodine Analogues
763
PO
HO
EtO
ref. 7
i
PO
O
O
O
H C N
3
H
3
OMe
4
5
Ethyl glycolate
P = TBDMS
ii
O
OEt
PO
CH3
iii
TBSO
CH3
PO
iv
OH
CO Et
7
6
2
H C
3
8
v
OH
PO
PO
vi
O
CH3
H C
3
H C
3
10
9
SCHEME 1 Synthesis of diene intermediate 10. Reagents: i) DIBAL-H, THF; ii) triethyl 2-
◦
◦
phosphonopropionate, NaH, THF, 0 C, 1 hour; iii) DIBAL-H, CH2Cl2, 0 C; iv) triethylorthoacetate,
◦
◦
propionic acid, 140 C; v) DIBAL-H, toluene, −78 C; vi) isopropenylMgBr, THF.
stage of Claisen rearrangement reaction. Ester 6 was reduced to allylic alco-
hol 7 by using diisobutylaluminum hydride (DIBAL-H), which underwent
[
9]
[
3,3]-sigmatropic rearrangement under Johnson-Claisen rearrangement
conditions to give γ ,δ–unsaturated ester 8. Direct reduction of the ester
8
to the aldehyde 9 was possible by slow addition of DIBAL-H in the
◦
toluene solvent system at –78 C. The aldehyde 9 was subjected to carbonyl
addition by isopropenyl Grignard reagent to yield divinyl 10 as inseparable
diastereomeric mixtures. Without separation, divinyl 10 was subjected to
standard ring-closing metathesis conditions using 2nd generation Grubbs
[
10]
catalyst
to provide cyclopentenol 11α and 11β, respectively. As shown in
Figure 2, the relative stereochemistry was readily determined on the basis of
the NOE results between the proximal hydrogens. On irradiation of C -H,
4
relatively weak nuclear overhauser enhancement (NOE) was observed at
C -H of 11(α) (0.09%), compared to that of 11(β) (0.32%).
1
For the synthesis β-configuration of nucleoside analogues, cyclopen-
tenol 11β was converted to 12 using ethyl chloroformate, which was coupled
with adenine or cytosine anions generated by NaH/DMSO with use of Pd(0)
catalyst adduct to provide carbocyclic nucleoside analogues 13 and 14. In
ꢁ
ꢁ
order to synthesize the 2 ,3 -dihydroxy carbocyclic nucleoside analogues 17

7
64
O. H. Ko and J. H. Hong
(
0.09%)
(0.32%)
OH
H
PO
PO
H
H
H
OH
CH3
1(α)
FIGURE 2 NOE data of compound 11(α) and 11(β).
H C
CH3
1(β)
3
H C
3
1
1
and 18, the double bonds of 13 and 14 were subjected to a catalytic amount
of OsO in the presence of stoichiometric amount of NMO to give the
4
[
11]
diol derivatives 15 or 16 as major products.
It is noteworthy that an
unexpected higher stereoselectivity was observed in this study than what was
reported in previously.[ These stereochemical outcomes suggest that the
bulky groups such as silylated hydroxymethyl group and nucleosidic base
of 13 and 14 reinforce the steric hindrance of the β-faces. Removals of
silyl protection group of 15 and 16 were preformed by the treatment of
tetrabutylammonium fluoride (TBAF) to give target carbodine analogues
12]
17 and 18 (Scheme 2).
The synthesized nucleoside analogues mentioned above were assayed
for their ability to inhibit HCV RNA replication in a subgenomic replicon
[
13]
cell line (Huh-7 cell line).
However, the nucleosides failed to inhibit
HCV RNA replication in the cell-based replicon assay (EC50 > µM).
OCO Et
PO
2
X
PO
i
ii
1
0
Y
CH
3
H C
3
CH
3
P = TBDMS
H C
3
12
1
1
1(β): X = OH, Y = H (36%)
1(α): X = H, Y = OH (37%)
iii
B
B
B
PO
PO
HO
H C
v
iv
H C
CH3
CH3
3
3
HO
OH
H C
3
CH
3
HO
OH
1
1
5: B = Adenine
6: B = Cytosine
1
1
7: B = Adenine
8: B = Cytosine
13: B = Adenine
14: B = Cytosine
ꢁ
ꢁ
SCHEME 2 Synthesis of 2 , 3 -C-dimethyl carbodine analogues. Reagents: i) 2nd-generation Grubbs
catalyst, benzene; ii) ethylchloroformate, DMAP, pyridine; iii) adenine and cytosine, Pd2(dba)3.
CHCL3, P(O-i-Pr)3, NaH, THF/DMSO, reflux, overnight; iv) OsO4, NMO, acetone/water; v) TBAF,
THF/CH3CN, room temperature.

ꢁ
ꢁ
Synthesis of Novel 2 ,3 -C-Dimethyl Carbodine Analogues
765
ꢁ
ꢁ
In summary, an efficient synthetic method of 2 ,3 -C-dimethylated carbo-
dine analogues from Weinreb amide was developed. We can conclude that
ꢁ
ꢁ
the dimethyl groups at 2 ,3 -position are attributed to the inability of the
nucleoside kinase to catalyze the initial phosphorylation of the nucleosides
to their monophosphates.
EXPERIMENTAL
Melting points were determined on a Mel-temp II laboratory device
and are uncorrected. NMR spectra were recorded on a JEOL 300 Fourier
transform spectrometer (JEOL, Tokyo, Japan); chemical shifts are reported
in parts per million (δ) and signals are reported as s (singlet), d (doublet),
t (triplet), q (quartet), m (multiplet), and dd (doublet of doublets). UV
spectra were obtained on a Beckman DU-7 spectrophotometer (Beckman,
South Pasadena, CA, USA). The elemental analyses were performed using
a Perkin-Elmer 2400 analyzer (Perkin-Elmer, Norwalk, CT, USA). TLC was
performed on Uniplates (silica gel) purchased from Analtech Co. (7558,
Newark, DE, USA). All reactions were carried out under an atmosphere
of nitrogen unless specified. Dry dichloromethane, benzene, and pyridine
were obtained by distillation from CaH . Dry THF was obtained by distilla-
2
tion from Na and benzophenone immediately prior to use.
(
t-Butyldimethylsilanyloxy) Acetaldehyde (5)
To a solution of Weinreb amide 4 (3.0 g, 12.85 mmol) in dry THF
(
0
60 mL) was slowly added DIBALH (15.42 mL, 1.0 M solution in Hexane) at
C. After 2 hours, methanol (15 mL) was added, and the reaction mixture
◦
was slowly warmed to room temperature. The mixture was stirred at room
temperature for 2 hours, and the resulting solid was filtered through a
Celite pad. The filtrate was concentrated under vacuum and the residue was
purified by silica gel column chromatography (EtOAc/hexane, 1:20) to give
crude aldehyde 5 (1.77 g, 79%) as colorless oil. Without further purification,
compound 5 was subject to next reaction.
(E) and (Z)-4-(t-Butyldimethylsilanyloxy)-2-methyl-but-2-enoic
Acid Ethyl Ester (6)
To a suspension of sodium hydride (400 mg, 9.98 mmol, 60% in
dispersion of oil) in distilled THF (50 mL) was added dropwise triethyl
◦
2
-phosphonopropionate (2.32 g, 9.98 mmol) at 0 C and the mixture was
stirred at room temperature for 1 hour. The aldehyde 5 (1.74 g, 9.98 mmol)
was added to this mixture and the mixture was for 2 hours. The solution
was neutralized with AcOH (2.0 mL) and poured into H O (100 mL) and
2
extracted with EtOAc (150 × 2). The combined organic layer was washed

7
66
O. H. Ko and J. H. Hong
with brine and dried over anhydrous MgSO , filtered, and evaporated. The
4
residue was purified by silica gel column chromatography (EtOAc/hexane,
1
1
:15) to give 6 (1.8 g, 70%) as a colorless oil: H NMR (CDCl , 300 MHz)
3
δ 6.20 (dd, J = 4.2, 1.8 Hz, 1H), 4.49 (m, 2H), 4.14 (q, J = 7.0 Hz, 2H),
1
3
1
(
.95 (s, 3H), 1.25 (t, J = 7.0 Hz, 3H), 0.83 (m, 9H), 0.01 (s, 6H); C NMR
CDCl ) δ 168.4, 137.9, 127.3, 67.3, 60.2. 25.5, 18.4, 17.2, 12.9, -5.5.
3
(E)and(Z)-3-(t-Butyldimethylsilyloxymethyl)-2-methyl-but-2-en-1-
ol(7)
To a solution of 6 (2.7 g, 10.5 mmol) in CH Cl (70 mL), DIBALH
2
2
◦
(
23.1 mL, 1.0 M solution in hexane) was added slowly at −20 C, and
stirred for 1 hour at the same temperature. To the mixture, methanol
23 mL) was added. The mixture was stirred at room temperature for 1
(
hour, and the resulting solid was filtered through a Celite pad. The filtrate
was concentrated under vacuum and the residue was purified by silica gel
column chromatography (EtOAc/hexane, 1:10) to give alcohol 7 (2.04 g,
1
9
1
0%) as a colorless oil: H NMR (CDCl , 300 MHz) δ 5.62 (dd, J = 4.0,
3
.6 Hz, 1H), 4.41–4.30 (m, 4H), 1.72 (s, 3H), 0.83 (m, 9H), 0.01 (m, 6H);
C NMR (CDCl ) δ 139.4, 122.2, 71.3, 65.3, 25.5, 18.4, 13.8, -5.6.
1
3
3
(
± )-3-(t-Butyldimethylsilyloxymethyl)-2-methyl-pent-4-enoic Acid
Ethyl Ester (8)
A solution of allylic alcohol 7 (3.4 g, 15.8 mmol) in triethyl orthoacetate
◦
(
60 mL) and 0.05 mL of propionic acid was heated at 140 C overnight with
stirring under condition for distillative removal of ethanol. The excess of
triethyl orthoacetate was distilled off and the residue was purified by silica
gel column chromatography (EtOAc/hexane, 1:20) to give 8 (3.62 g, 80%)
1
as a colorless oil: H NMR (CDCl , 300 MHz) δ 5.63–5.55 (m, 2H), 4.09 (q, J
3
=
7.0 Hz, 2H), 3.53 (d, J = 9.6 Hz, 1H), 3.42 (d, J = 9.6 Hz, 1H), 2.60 (dd,
J = 14.0, 5.2 Hz, 1H), 2.36 (dd, J = 14.0, 8.6 Hz, 1H), 2.27 (m, 1H), 1.79 (s,
13
3
H), 1.23 (t, J = 7.0 Hz, 3H), 0.83 (s, 9H), 0.01 (s, 6H); C NMR (CDCl )
3
δ 172.4, 139.4, 118.2, 66.4, 61.8, 45.9, 40.3, 25.7, 18.6, 17.4, 13.6, -5.6.
(± )-3-(t-Butyldimethylsilyloxymethyl)-2-methyl-pent-4-enal (9)
To a solution of 8 (3.0 g, 10.5 mmol) in toluene (50 mL), DIBALH
◦
(
7.7 mL, 1.5 M solution in toluene) was added slowly at −78 C, and
stirred for 10 minutes at the same temperature. To the mixture, methanol
(8 mL) was added. The mixture was stirred at room temperature for 1
hour, and the resulting solid was filtered through a Celite pad. The filtrate
was concentrated under vacuum and the residue was purified by silica gel
column chromatography (EtOAc/hexane, 1:15) to give 9 (2.54 g, 63%) as a

ꢁ
ꢁ
Synthesis of Novel 2 ,3 -C-Dimethyl Carbodine Analogues
767
1
colorless oil: H NMR (CDCl , 300 MHz) δ 9.71 (s, 1H), 5.60–5.53 (m, 2H),
3
3
2
0
4
.62 (dd, J = 9.8, 5.0 Hz, 1H), 3.45 (d, J = 9.6, 5.6 Hz, 1H), 2.70 (m, 1H),
.61 (dd, J = 13.6, 5.4 Hz, 1H), 2.39 (dd, J = 13.6, 5.6 Hz, 1H), 1.76 (s, 3H),
13
.82 (s, 9H), 0.01 (s, 6H); C NMR (CDCl ) δ 202.1, 140.7, 119.7, 69.5, 61.8,
3
6.1, 41.6, 25.7, 18.7, 17.9, -5.5.
(
rel)-(3R and 3S,5S)-5-(t-Butyldimethylsilanyloxymethyl)-2,6-
dimethyl-hepta-1,6-dien-3-ol(10)
To a solution of 9 (1.33 g, 5.5 mmol) in dry THF (25 mL) was slowly
added isopropenylmagnesium bromide (13.2 mL, 0.5 M solution in THF) at
◦
−
40 C. After 5 hours, saturated NH Cl solution (7 mL) was added, and the
4
reaction mixture was slowly warmed to room temperature. The mixture was
extracted with EtOAc/water twice. The combined organic layer was dried
over MgSO , filtered, and evaporated. The residue was purified by silica gel
4
column chromatography (EtOAc/hexane, 1:15) to give 10 (1.24 g, 79%) as
1
a diastereomeric mixture: H NMR (CDCl , 300 MHz) δ 5.13 (s, 1H), 5.04
3
(s, 1H), 4.93 (s, 1H), 4.81 (s, 1H), 3.99–3.88 (m, 1H), 3.45–3.30 (m, 2H),
2
9
1
.21–2.09 (m, 1H), 1.69 (s, 3H), 1.52 (s, 3H), 1.50–1.41 (m, 2H), 0.81 (s,
13
H), 0.01 (m, 6H); C NMR (CDCl ) δ 147.5, 142.3, 139.0, 117.7, 116.6,
3
10.4, 77.3, 72.5, 66.1, 51.76, 38.5, 25.7, 20.32, 18.6, 17.3, -5.6.
(
rel)-(1R,4S)-4-(t-Butyldimethylsilyloxymethyl)-2,3-dimethyl-
cyclopent-2-enol(11β);and(rel)-(1S,4S)-4-(t-
Butyldimethylsilyloxymethyl)-2,3-dimethyl-cyclopent-2-enol(11α)
To a solution of 10 (3.51 g, 12.36 mmol) in dry benzene (15 mL)
was added second generation Grubbs catalyst (183 mg 0.216 mmol). The
reaction mixture was refluxed overnight, and cooled to room temperature.
The mixture was concentrated in vacuum, and residue was purified by silica
gel column chromatography (EtOAc/hexane, 1:12) to give cyclopentenol
1
1β (1.14 g, 36%) and 11α (1.17 g, 37%) as colorless oils, respectively.
1
Cyclopentenol 11β: H NMR (CDCl , 300 MHz) δ 4.31 (dd, J = 10.2, 7.8
3
Hz, 1H), 3.90 (d, J = 8.8 Hz, 1H), 3.79 (d, J = 9.0 Hz, 1H), 2.90 (m, 1H),
2
.61 (d, J = 10.6 Hz, 1H), 2.20 (dd, J = 13.8, 7.4 Hz, 1H), 1.65 (s, 3H), 1.22
13
(s, 3H), 0.81 (s, 9H), 0.01 (s, 6H): C NMR (CDCl ) δ 138.8, 135.6, 78.2,
3
67.3, 49.2, 38.8, 25.5, 18.5, 11.6, 10.8, -5.5; Anal. Calcd. for C H O Si: C,
14 28 2
6
5.57; H, 11.00. Found: C, 65.65; H, 10.91.
1
Cyclopentenol 11α: H NMR (CDCl , 300 MHz) δ 4.52 (s, 1H), 3.94 (d,
3
J = 9.2 Hz, 1H), 3.75 (d, J = 9.1 Hz, 1H), 2.87 (m, 1H), 2.60 (dd, J = 13.8,
7
.8 Hz, 1H), 1.74 (s, 3H), 1.65 (dd, J = 13.8, 6.0 Hz, 1H), 1.33 (s, 3H), 0.82
13
(s, 9H), 0.01 (s, 6H): C NMR (CDCl ) δ 137.9, 135.0, 77.8, 67.8, 48.9, 39.6,
3
2
5.6, 18.6, 11.1, 10.4, -5.6; Anal. Calcd. for C H O Si: C, 65.57; H, 11.00.
14 28 2
Found: C, 65.48; H, 11.07.

7
68
O. H. Ko and J. H. Hong
(
rel)-(1R,4S)-1-Ethoxy carbonyloxy-4-(t-
butyldimethylsilyloxymethyl)-2,3-dimethyl-cyclopent-2-ene(12)
To a solution of 11β (3.19 g, 12.45 mmol) in anhydrous pyridine
(
(
25 mL) was added ethyl chloroformate (2.68 g, 24.7 mmol) and DMAP
122 mg, 1.0 mmol). The reaction mixture was stirred overnight at 50 C.
◦
The reaction mixture was quenched with saturated NaHCO solution (6
3
mL), stirred for 10 minutes and concentrated in reduced pressure. The
residue was extracted with EtOAc/H O two times, and combined organic
2
layer was dried over MgSO , filtered, and concentrated. The residue was
4
purified by silica gel column chromatography (EtOAc/hexane, 1:20) to give
1
1
2 (3.06 g, 75%) as colorless syrup: H NMR (CDCl , 300 MHz) δ 5.03 (dd,
3
J = 6.2, 4.2 Hz, 1H), 4.15 (q, J = 7.4 Hz, 2H), 3.45 (m, 2H), 2.34 (m, 1H),
2
.20 (dd, J = 13.8, 8.2 Hz, 1H), 1.91 (s, 3H), 1.70 (dd, J = 13.8, 3.6 Hz, 1H),
13
1
.52 (s, 3H), 1.27 (t. J = 7.4 Hz, 3H), 0.82 (s, 9H), 0.01 (s, 6H): C NMR
(CDCl ) δ 155.5, 138.0, 134.5, 85.8, 66.9, 64.8, 51.3, 40.3, 25.4, 18.3, 12.3,
3
1
0.8, -5.5; Anal. Calcd. for C H O Si: C, 62.15; H, 9.82. Found: C, 62.23;
17 32 4
H, 9.92.
ꢁ
ꢁ
(
rel)-(1 R,4 S)-9-[4-(t-Butyldimethylsilyloxymethyl)-2,3-dimethyl-
cyclopent-2-en-1-yl]adenine(13)
In order to generate nucleosidic base anion, adenine (194 mg,
.13 mmol) was added to a hexane washed NaH (30.2 mg, 1.26 mmol) in
1
anhydrous DMSO (7.0 mL). The reaction mixture was stirred for 40 minutes
◦
at 50–55 C and cooled to room temperature. Simultaneously, P(O-i-Pr)3
(
93 mg, 0.45 mmol) was added to a solution of Pd (dba) · CHCl (58
2
3
3
mg, 5.65 µmol) in anhydrous THF (7.0 mL), which was stirred for 30
minutes. To the adenine solution of DMSO was sequentially added catalyst
solution of THF and 12 (345 mg, 1.05 mmol) dissolved in anhydrous THF
(8.0 mL). The reaction mixture was stirred overnight at refluxing tempera-
ture and quenched with water (4.0 mL). The reaction solvent was removed
in vacuum. The residue was purified by silica gel column chromatography
(
MeOH/Hexane/EtOAc, 0.1:5:1) to give 13 (137.3 mg, 35%) as a white
◦
; 1
solid; m.p. 180–182 C H NMR (CDCl , 300 MHz) δ 8.27 (s, 1H), 8.11 (s,
3
1
8
1
H), 4.86 (dd, J = 8.0, 4.6 Hz, 1H), 3.69 (d, J = 8.8 Hz, 1H), 3.49 (d, J =
.8 Hz, 1H), 2.49 (m, 1H), 2.36 (dd, J = 13.6, 6.8 Hz, 1H), 2.09 (dd, J =
3.6, 8.6 Hz, 1H), 1.71 (s, 3H), 1.62 (s, 3H), 0.81 (s, 9H), 0.01 (s, 6H): 13
C
NMR (CDCl ) δ 155.6, 152.3, 148.6, 141.2, 138.1, 132.2, 118.2, 67.7, 66.1,
3
5
0.5, 46.8, 25.3, 23.6, 18.4, 13.4, 11.3, -5.6; Anal. Calcd. for C H N OSi: C,
19 31 5
61.09; H, 8.36; N, 18.75. Found: C, 60.89; H, 8.41; N, 18.62.

ꢁ
ꢁ
Synthesis of Novel 2 ,3 -C-Dimethyl Carbodine Analogues
769
ꢁ
ꢁ
(
rel)-(1 R,4 S)-1-[4-(t-Butyldimethylsilyloxymethyl)-2,3-dimethyl-
cyclopent-2-en-1-yl]cytosine(14)
Cytosine nucleoside 14 analogue was synthesized from 12 by the similar
◦
1
procedure as described for 13: yield 36%; m.p. 181–183 C; H NMR (CDCl ,
3
3
7
1
00 MHz) δ 7.37 (d, J = 7.2 Hz, 1H), 5.80 (d, J = 4.2 Hz, 1H), 5.42 (d, J =
.2 Hz, 1H), 3.77 (d, J = 8.4, Hz, 1H), 3.51 (d, J = 8.4 Hz, 1H), 2.95 (m,
H), 2.71 (dd, J = 13.6, 7.6 Hz, 1H), 2.15 (dd, J = 13.6, 2.4 Hz, 1H), 1.75
(
s, 3H), 1.32 (s, 3H), 0.83 (s, 9H), 0.02 (s, 6H): 13C NMR (CDCl ) δ 165.5,
3
155.6, 143.1, 140.4, 133.1, 94.1, 67.5, 58.3, 41.6, 25.5, 18.5, 11.2, 10.1, -5.6;
Anal. Calcd. for C H N O Si: C, 61.85; H, 8.94; N, 12.02. Found: C, 61.92;
18
31
3
2
H, 8.89; N, 11.98.
ꢁ
ꢁ
ꢁ
ꢁ
(
rel)-(1 R,2 S,3 R,4 R)-9-[4-(t-Butyldimethylsilyloxymethyl)-2,3-
dimethyl-2,3-dihydroxy-cyclopentan-1-yl]adenine(15)
To a stirred solution of 13 (376 mg, 1.008 mmol) in cosolvent (4.0
mL, acetone:water/5:1) was added NMO (236 mg, 2.016 mmol), and OsO4
◦
(
0.06 mL, 4% in water). The mixture was stirred overnight at 50 C, and
quenched with saturated Na SO solution (4 mL). Resulting solid was
2
3
removed by filtration through a pad of Celite, and filtrate was concentrated
in reduced pressure. The residue was purified by silica gel column chro-
matography (MeOH/CH Cl , 1:7) to give 15 (291 mg, 71%) as a white solid:
2
2
◦
1
m.p. 194–196 C; H NMR (DMSO-d , 300 MHz) δ 8.31 (s, 1H), 8.19 (s, 1),
6
7
.19 (br s, 2H, D O exchangeable), 5.17 (s, 1H, D O exchangeable), 5.09
2
2
(
1
s, 1H, D O exchangeable), 5.08 (dd, J = 5.2, 2.4 Hz, 1H), 3.46 (dd, J =
2
2.6, 7.2 Hz, 1H), 3.30 (dd, J = 12.6, 8.4 Hz, 1H), 2.44 (dd, J = 10.6, 4.2
Hz, 1H), 2.31 (dd, J = 10.6, 8.6 Hz, 1H), 1.60 (m, 1H), 1.41 (s, 3H), 1.23 (s,
13
3
H), 0.82 (s, 9H), 0.01 (s, 6H): C NMR (DMSO-d ) δ 155.7, 152.0, 149.7,
6
140.5, 119.4, 83.3, 81.3, 69.7, 56.7, 25.6, 18.4, 17.1, 16.2, 14.3, -5.7; Anal calc
for C H N O Si: C, 55.99; H, 8.16; N, 17.18. Found: C, 56.13; H, 8.03; N,
19
33
5
3
17.23.
ꢁ
ꢁ
ꢁ
ꢁ
(
rel)-(1 R,2 S,3 R,4 R)-1-[4-(t-Butyldimethylsilyloxymethyl)
2,3-dimethyl-2,3-dihydroxy-cyclopentan-1-yl] cytosine (16)
Cytosine nucleoside 16 analogue was synthesized from 14 by the similar
◦
1
procedure as described for 15: yield 69%; m.p. 189–192 C; H NMR (DMSO-
d , 300 MHz) δ 7.65 (d, J = 7.2 Hz, 1H), 7.05 (br d, 2H, D O exchangeable),
6
2
5
5
1
.59 (d, J = 7.2 Hz, 1H), 5.12 (s, J = 4.6 Hz, 1H, D O exchangeable),
2
.02 (s, 1H, D O exchangeable), 4.97 (m, 1H), 3.71 (dd, J = 13.2, 6.6 Hz,
2
H), 3.42 (dd, J = 13.2, 8.8 Hz, 1H), 2.19 (dd, J = 13.2, 4.8 Hz, 1H), 1.97
(
dd, J = 13.2, 8.0 Hz, 1H), 1.63 (m, 1H), 1.47 (s, 3H), 0.82 (s, 9H), 0.01
(
s, 6H): 13C NMR (DMSO-d ) δ 165.5, 156.6, 144.3, 94.2, 83.2, 81.3, 62.7,
6

7
70
O. H. Ko and J. H. Hong
5
7.9, 41.3, 25.5, 18.7, 17.3, 13.5, 12.5, -5.6; Anal. Calcd. for C H N O Si:
18
33
3
4
C, 56.37; H, 8.67; N, 10.96. Found: C, 56.43; H, 8.71; N, 11.04.
ꢁ
ꢁ
ꢁ
ꢁ
(
rel)-(1 R,2 S,3 R,4 R)-9-[4-(Hydroxymethyl)-2,3-dimethyl-2,3-
dihydroxy-cyclopentan-1-yl]adenine(17)
To a solution of 15 (171 mg, 0.42 mmol) in cosolvent (5.0 mL,
THF:CH CN/1:1) THF (5 mL) was TBAF (0.63 mL, 1.0 M solution in
3
◦
THF) at 0 C. The mixture was stirred overnight at room temperature, and
concentrated. The residue was purified by silica gel column chromatogra-
phy (MeOH/CH Cl , 1:4) to give 17 (76 mg, 70%) as a white solid: m.p.
2
2
◦
1
2
08–210 C; UV (H O) λ
259.5 nm; H NMR (DMSO-d , 300 MHz) δ
2
max 6
8
.32 (s, 1H), 8.12 (s, 1H), 7.20 (br s, 2H, D O exchangeable), 5.09 (s, 1H,
2
D O exchangeable), 5.01 (s, 1H, D O exchangeable), 4.92 (m, 1H), 4.81
2
2
(
t, J = 4.6 Hz, 1H, D O exchangeable), 3.51–3.39 (m, 2H), 2.20 (dd, J =
2
1
3
8
3.2, 4.4 Hz, 1H), 2.04 (dd, J = 13.2, 8.6 Hz, 1H), 1.69 (m, 1H), 1.40 (s,
13
H), 1.32 (s, 3H); C NMR (DMSO-d ) δ 155.3, 152.2, 147.6, 137.3, 118.6,
6
2.1, 80.4, 68.2, 56.2, 40.2, 16.0, 13.9, 12.1; Anal calc for C H N O +1.0
13
19
5
3
H O: C, 50.15; H, 6.79; N, 22.49. Found: C, 50.03; H, 6.81; N, 22.39.
2
ꢁ
ꢁ
ꢁ
ꢁ
(
rel)-(1 R,2 S,3 R,4 R)-1-[4-(t-Hydroxymethyl)-2,3-dimethyl-
cyclopent-2-en-1-yl]cytosine(18)
Cytosine nucleoside 18 analogue was synthesized from 16 by the similar
condition as described for 17 as a white solid as a white solid: yield 73%; m.p.
◦
1
1
97–199 C; UV (H O) λ
271.5 nm; H NMR (DMSO-d , 300 MHz) δ 7.68
2
max 6
(
1
d, J = 7.3 Hz, 1H), 7.11 (br d, 2H, D O exchangeable), 5.60 (d, J = 7.2 Hz,
2
H), 5.09 (s, 1H, D O exchangeable), 5.00 (s, 1H, D O exchangeable), 4.89
2
2
(
m, 1H), 4.80 (t, J = 4.2 Hz, 1H), 3.54 (dd, J = 13.2, 4.8 Hz, 1H), 3.30 (dd,
J = 13.2, 8.0 Hz, 1H), 2.19–2.08 (m, 2H), 1.70 (m, 1H), 1.37 (s, 3H), 1.30 (s,
3
4
7
H): 13C NMR (DMSO-d ) δ 165.8, 155.5, 145.1, 95.5, 81.1, 80.3, 68.2, 56.2,
6
1.3, 15.6, 14.3, 13.2,; Anal. Calcd. for C H N O +1.0 H O: C, 50.16; H,
12
19
3
4
2
.36; N, 14.62. Found: C, 50.25; H, 7.27; N, 14.54.
REFERENCES
1. Tan, S.L.; Pause, A.; Shi, Y.; Sonenberg, N. Hepatitis C therapeutics: current status and emerging
strategies. Nat. Rev. Drug Discovery 2002, 1, 867–881.
2
. Heathcote, E.; Shiffman, M.; Cooksley, W.; Dusheiko, G.M.; Lee, S.S.; Balart, L.; Reindollar, R.;
Reddy, R.K.; Wright, T.L.; Lin, A.; Hoffman, J.; De Pamphilis, J. Peginterferon alfa-2a in patients
with chronic hepatitis C and cirrhosis. N. Engl. J. Med. 2000, 343, 1673–1680.
3
. a) Bera, S.; Malik, L.; Bhat, B.; Carroll, S.S.; MacCoss, M.; Olsen, D.B.; Tomassini, J.E.; Eldrup,
A.B. Synthesis and evaluation of optically pure dioxolanes as inhibitors of hepatitis C virus RNA
replication. Bioorg. Med. Chem. Lett. 2003, 13, 4455–4458; b) Eldrup, A.B.; Prhavc, M.; Brooks, J.;
Bhat, B.; Prakash, T.P.; Song, Q.; Bera, S.; Bhat, N.; Dande, P.; Cook, P.D.; Bennett, C.F.; Carroll,
S.S.; Ball, R.G.; Bosserman, M.; Burlein, C.; Colwell, L.F.; Fay, J.F.; Flores, O.A.; Getty, K.; LaFemina,

ꢁ
ꢁ
Synthesis of Novel 2 ,3 -C-Dimethyl Carbodine Analogues
771
R.L.; Leone, J.; MacCoss, M.; McMasters, D.R.; Tomassini, J.E.; Von Langen, D.; Wolanski, B.; Olsen,
ꢁ
D.B. Structure-activity relationship of heterobase-modified 2 -C-methyl ribonucleosides as inhibitors
of hepatitis C virus RNA replication. J. Med. Chem. 2004, 47, 5284–5297; c) Clark, J.L.; Hollecker, L.;
Mason, J.C.; Stuyver, L.J.; Tharnish, P.M.; Lostia, S.; McBrayer, T.R.; Schinazi, R.F.; Watanabe, K.A.;
Otto, M.J.; Furman, P.A.; Stec, W.J.; Patterson, S.E.; Pankiewicz, K.W. Design, synthesis, and antiviral
ꢁ
ꢁ
ꢁ
activity of 2 -deoxy-2 -fluoro-2 -C-methylcytidine, a potent inhibitor of hepatitis C virus replication.
J. Med. Chem. 2005, 48, 5504–5508. d) Smith, D.B.; Kalayanov, G.; Sund, C.; Winqvist, A.; Pinho,
P.; Maltseva, T.; Morisson, V.; Leveque, V.; Rajyaguru, S.; Le Pogam, S.; Najera, I.; Benkestock, K.;
Zhou, X.X.; Maag, H.; Cammack, N.; Martin, J.A.; Swallow, S.; Johansson, N.G.; Klumpp, K.; Smith,
ꢁ
M. The design, synthesis, and antiviral activity of 4 -azidocytidine analogues against hepatitis C virus
ꢁ
replication: the discovery of 4 -azidoarabinocytidine. J. Med. Chem. 2009, 52, 219–223.
4. El Kouni, M.H. Trends in the design of nucleoside analogues as anti-HIV drugs. Curr. Pharm. Des.
2002, 8, 581–593.
5
. Carrol, S.S.; Tomassini, J.E.; Bosserman, M.; Getty, K.; Stahlhut, M.W.; Eldrup, A.B.; Bhat, B.; Hall,
D.; Simcoe, A.L.; LaFemina, R.; Rutkowski, C.A.; Wolanski, B.; Yang, Z.; Migliaccio, G.; De Francesco,
R.; Kuo, L.C.; MacCoss, M.; Olsen, D.B. Inhibition of hepatitis C virus RNA replication by 2 -modified
ꢁ
nucleoside analogs. J. Biol. Chem. 2003, 278, 11979–11984.
6
. Eldrup, A.B.; Allerson, C.R.; Bennett, C.F.; Bera, S.; Bhat, B.; Bhat, N.; Bosserman, M.R.; Brooks,
J.; Burlein, C.; Carrol, S.S.; Cook, P.D.; Getty, K.L.; MacCoss, M.; McMasters, D.R.; Olsen, D.B.;
Prakash, T.P.; Prhavc, M.; Song, Q.L.; Tomassini, J.E.; Xia, J. Structure-activity relationship of purine
ribonucleosides for inhibition of hepatitis C virus RNA-dependent RNA polymerase. J. Med. Chem.
2
004, 47, 2283–2295.
ꢁ
7
8
9
. Liu, L.J.; Yoo, J.C.; Hong, J.H. Efficient synthesis of 4 -cyclopropylated carbovir analogues with use
of ring-closing metathesis from glycolate. Nucleosides Nucleotides Nucleic Acids 2008, 27, 1186–1196.
. Hyatt, J.A. Convenient monoketalization of 1,4-cyclohexanedione. Synthesis of new quinone me-
thides. J. Org. Chem. 1983, 48, 129–131.
. a) Johnson, W.S.; Werthmann, L.; Bartlett, W.R.; Brocksom, T.J.; Li, T.T.; Faulkner, D.J.; Petersen,
M.R. Simple stereoselective version of the Claisen rearrangement leading to trans-trisubstituted
olefinic bonds. Synthesis of squalene. J. Am. Chem. Soc. 1970, 92, 741–743; b) Castro, A.M.M. Claisen
rearrangement over the past nine decades. Chem. Rev. 2004, 104, 2939–3002; c) Ziegler, F.E. The
thermal, aliphatic Claisen rearrangement. Chem. Rev. 1988, 88, 1423–1452; d) Lutz, R. Catalysis of
the Cope and Claisen rearrangements. Chem. Rev. 1984, 84, 205–297.
1
0. a) Furstner, A. Olefin metathesis and beyond. Ange. Chem. Int. Ed. Engl. 2000, 39, 3012–3043;
b) Nicolaou, K.C.; Bulger, P.G.; Sarlah, D. Metathesis reactions in total synthesis. Ange. Chem. Int.
Ed. Engl. 2005, 44, 4490–4527; c) Hansen, E.C.; Lee, D. Search for solutions to the reactivity and
selectivity problems in enyne metathesis. Acc. Chem. Res. 2006, 39, 509–519.
1
1
1
1. Hong, J.H.; Shim, M.J.; Ro, B.O.; Ko, O.H. An efficient synthesis of novel carbocyclic nucleosides
with use of ring-closing metathesis from D-lactose. J. Org. Chem. 2002, 67, 6837–6840.
2. Burlina, F.; Favre, A.; Fourrey, J.-L.; Thomas, M. An expeditious route to carbocyclic nucleosides:
(
−)-aristeromycin and (−)-carbodine. Bioorg. Med. Chem. Lett. 1997, 7, 247–250.
3. Stuyver, L.J.; McBrayer, T.R.; Tharnish, P.M.; Hassan, A.E.A.; Chu, C.K.; Pankiewicz, K.W.; Watanabe,
K.A.; Schinazi, R.F.; Otto, M.J. Dynamics of subgenomic hepatitis C virus replicon RNA levels in
Huh-7 cells after exposure to nucleoside antimetabolite. J. Virol. 2003, 77, 10689–10694.